Mold



Patented Feb. 14, 1939 UNITED STATES PATENT OFFICE derus'scheEisenwerke, Wetzlar,

Germany, a

corporation of Germany,

Application December 8, 1936, Serial No. 114,865 In Germany December 10,1935 1 Claim. (01. 22-65) This invention relates to molds, particularlymolds in which hot melts, for example cast iron or steel melts, are tobe poured in the manufacture of centrifugally cast articles. The innersurface of such molds tends to crack owing to the high stresses to whichit is subjected in opera-- tion, and various ways have been tried tocounteract this deficiency. For example, it has been proposed to usehigh grade alloys to make the molds, or to harden their inner surfacesby the nitrating method. It has also been proposed to protect the moldsby dusting them with various protective materials before each castingoperation. Still another prior proposition is to make v the molds of aplurality of tubes drawn one over the other and having differentcoeflicients of heat expansion.

The present invention relates to molds of this last mentioned kind andit consists in providing a mold in which the layers of material ofdifferent heat expansioncapacity are welded together, the outer layerpreferably having the greater heat expansion coemcient. This makes itpossible to put the inner layer of the mold not only under compression,but also under tension, according to requirements, and thus to maintaina secure connection of the difierent layers.

The invention also comprises a method of making such molds according towhich an outer layer is first centrifuged into place and an inner layerof material of different heat expansion capacity is centrifuged indirect sequence on said first layer.

In some cases the inner layer of the mold is made of material of greaterheat expansion :apacity than the outer layer. With increasing aeating ofthe mold the inner layerwill be put inder compression increasing withthe temperiture. If desired a mold may be used the inner ayer of whichhas already been given an initial :ompression. In molds of this latterkind the :onnection of the layers of different heat expanaion capacitymay be efiected in another manier, for example, by shrinking. Since theheat expansion coeflicient of different materials does lot vary inlinear proportion when the range of temperature is iarge, but vary indifferent ways within certain temperature ranges, it is possible toprepare molds, according to the present invention, in which the tensionof the inner layer, with rising temperature, does not vary continuouslyin the one direction, but in different directions, that is firstincreases and then decreases or vice versa, or following an, increase ora decrease, may maintain approximately the same value upon a furthervariation of the temper- Fig. 2 is a longitudinally sectional view ofthe 25 mold. r

The mold I is composed of an inner layer 2 and an outer layer 3. Theselayers are made of metal of different heat expansion capacity andalthough the layers are welded together the layers are shown as havingdifferent cross hatching to illustrate the layers of metal of which thelayer 2 is under tension at room temperature but which changes tocompression at higher temperatures. v

I claim as my invention: A mold for making centrifugally cast articles,comprising inner and outer layers of metal of different heat expansioncapacity, the inner layer being centrifugally welded to the outer layerand having a greater heat expansion capacity than said outer layer,whereby the inner layer under tension at room temperature which changesto compression at higher temperatures.

ERNST roan

